A power converter comprising a plurality of pairs of electrical valve bridges which have a plurality of electrical valves connected in each bridge between DC terminals and AC terminals connected to an AC load and a plurality of controllable DC power means for feeding pulsating unidirectional current into the DC terminals of the electrical valve bridges or out of the DC terminals whereby the unidirectional pulsating current is distributed to the plurality of pairs of electrical valve bridges for feeding to the AC load. The power converter further comprises magnetically coupled reactors connected in unidirectional pulsating current lines. Alternatively, it further comprises DC lines of the unidirectional pulsating current lines which are connected as a common lines.
A portable power unit has a magneto generator having three-phase output windings. A synchronizing signal is formed in synchronism with an output frequency of the magneto generator. A pair of variable control bridge circuits are connected to the three-phase output windings and connected in antiparallel connection to each other to form a cycloconverter for generating a single-phase alternating current having a desired frequency to be supplied to a load. A bridge drive circuit is responsive to the synchronizing signal from the synchronizing signal-forming circuit, for causing the pair of variable control bridge circuits to be alternately switched to operate every half a repetition period of the single-phase alternating current, to thereby cause the cycloconverter to generate the single-phase alternating current. An output voltage-detecting circuit detects an output voltage of the pair of variable control bridge circuits. An output voltage-adjusting circuit compares the output voltage detected by the output voltage-detecting circuit with a desired voltage to thereby control the bridge drive circuit in a manner such that the output voltage of the pair of variable control bridge circuits is maintained substantially at a fixed value.
A load commutated inverter (LCI) a-c drive system includes a synchronous motor with two 30 degree angularly displaced sets of three-phase windings. Each set of motor windings is powered by a three-phase inverter fed by a three-phase rectifier in a separate d-c loop. The three-phase rectifiers are fed by either a generator with two angularly displaced sets of three-phase windings or by a transformer with a three-phase primary winding, and delta and wye secondary windings separately supplying the two rectifiers. Twelve-pulse operation in the line commutated mode with substantially constant d-c link currents significantly reduces torque pulsations. At low speeds, sinusoidal segment pulsed d-c currents in the d-c links are gated to pairs of windings in the two sets of motor windings which generate component MMFs either 90 degrees or 150 degrees displaced to produce a resultant rotating motor MMF of constant magnitude to completely eliminate torque pulsations. Since the repetition rates of the pulsed d-c link currents in these two instances are 2 and 1.2 times the fundamental motor frequency respectively, the range of motor speeds over which torque pulsations can be completely eliminated is substantially increased, while torque pulsations at all higher speeds are greatly reduced.
A power converter apparatus has at least two converters CONV1 and CONV2. The DC side of each of the converters CONV1 and CONV2 is connected to a filtering capacitor Cd which serves as a DC power source for a load device LOAD. The AC side of the converter CONV1 is connected to the secondary winding of a first transformer TR1. The AC side of the converter CONV2 is connected to the secondary winding of a second transformer TR2. The primary winding of transformer TR1 is connected in series to the primary winding of transformer TR2. The series circuit of the primary windings of transformers TR1 and TR2 is coupled to an AC power supply SUP via a single AC reactor Ls. A control method of the invention is adapted to the power converter apparatus in which plural PWM converters are used. The phase of a modulating wave (carrier) of one PWM converter differs by a predetermined degree from that of another PWM converter.
A first static commutator including a first controllable thyristor rectifier and a first thyristor inverter and a second static commutator including a second controllable thyristor rectifier and a second thyristor inverter are provided. First three-phase AC voltage is supplied to the first controllable rectifier, and second three-phase AC voltage 30 degrees out of phase with said first three-phase AC voltage is supplied to the second controllable rectifier. A brushless motor includes first star-connected three-phase windings receiving the output of the first inverter and second star-connected three-phase windings and 30 degrees out of phase with said first three phase windings. During the starting period of the brushless motor the conduction of the first and second satic commutators is switched for every 30-degree rotation of the brushless motor.
A frequency changer having parallel partial frequency changers with a dc circuit has chokes that impress dc currents. These chokes are magnetically coupled to each other such that the change of a dc current in one of the partial frequency changers causes a corresponding change of the dc currents in the parallel partial frequency changer in the sense of a lead control. In a frequency changer constructed with an even number of partial frequency changers, the individual chokes can be coupled such that the magnetic dc fluxes in the coupling caused by the dc currents in the chokes are compensated.
